One part of the tyrosine hydroxylase story that is still missing is the structure of the 150 amino acid regulatory domain at the N-terminus of the protein. A plasmid for producing the human holoenzyme has been supplied to the Stevens lab by Jan Haavik of the University of Bergen. Hopefully, biochemical techniques for protein stability developed for previous Stevens lab studies of tyrosine hydroxylase will allow for the growth of diffraction quality crystals of the whole enzyme. These crystallization trials are underway. The atomic interactions which we are looking for in the tyrosine hydroxylase complexes will only be visible by using high resolution x-ray data. Since the molecular features of interest will only be seen using data better than 2.5 E resolution, the use of high-brilliance synchrotron radiation will be vital for the structural studies of this enzyme.